In general, a motor is divided to a rotary motor for changing electric energy into rotary movement, reciprocating motor which changes electric energy into linear reciprocating movement, and the like.
Particularly, in the reciprocating motor an outer stator and inner stator are positioned a predetermined interval apart from each other and a rotor having a magnet between the outer and inner stators. When a power is applied to a coil which is wound on the stator, the rotor preforms a linear reciprocating movement by interaction between the stator and magnet. The reciprocating motor is commonly used for a reciprocating compressor.
FIG. 1 is a cross-sectional view showing a conventional reciprocating motor.
The conventional reciprocating motor includes a cylindrical outer stator 102 which is fixed to a housing (not shown), an inner stator 104 positioned having a predetermined air gap on the inner circumferential surface of the outer stator 102, for forming a flux between itself and the outer stator 102, a coil 106 which is wound in the inner portion of the outer stator 102, a magnet 108 which is positioned between the outer stator 102 and inner stator 104, capable of performing a linear movement, a magnet frame 110 connected between the magnet 108 and a component part (not shown) ch will perform reciprocating movement, for transmitting the reciprocating movement of the magnet 108 to the component part.
The outer stator 102 is formed in a cylindrical shape by layering a plurality of ironic cores and a coil 106 is wound in the inner side of the outer stator 102. The inner stator 104 is formed in a cylindrical shape by layering a plurality of ironic cores having a predetermined gap L on an inner circumferential surface of the outer stator 102. The coil 106 forms a flux between the outer stator 102 and inner stator 104 when a power is applied from the outside and fixed rings 120 and 124 for fixing layered iron cores are respectively mounted in the outer stator 102 and inner stator 104.
As shown in FIG. 2, the magnet frame 110 is formed in a cylindrical shape between the outer stator 102 and inner stator 104 capable of performing a reciprocating movement and the thickness of the magnet frame 110 must be formed as thin as possible to minimize the air gap L between the outer stator 102 and inner stator 104. Accordingly, conventionally, the magnet frame 110 is manufactured by molding methods such as sheet metal forming, compression or die casting of non-magnetic metal material.
As shown in FIG. 2, the magnet frame 110 includes a magnet mounting portion 112 in which the magnet 108 is mounted at a uniform interval in the direction circumference of a side portion positioned between the outer stator 102 and inner stator 104, and a connecting portion 116 in which a plurality of air passes 114 are formed in the circumferential direction at the other side of the magnet frame 110, and which transmits a reciprocating moving force to an operating unit (not shown) which will perform a linear reciprocating movement.
In the magnet mounting portion 112, magnets 108 having a predetermined width and length are fixed at a predetermined interval in the circumferential direction and a slit 118 for preventing eddy current loss by the magnet 108 is formed in the magnet mounting portion 112.
The slit 118 intercepts loss of the current which flows in the circumferential direction of the magnet frame 110 when the magnet 108 performs a linear reciprocating movement and prevents lowering of motor efficiency according to eddy current loss. The slit 118 is formed protruded in the shape of stripe having a narrow width in the stroke direction of the magnet 108.
The operation of the conventional reciprocating motor with the above composition will be described as follows.
When the power is applied to the coil 110, a flux is formed around the coil 110 and the flux forms a closed loop along the outer stator 106 and inner stator 108. The magnet 112 linearly moves in the direction of shaft by the interaction between the flux generated between the outer stator 106 and inner stator 108 and the flux generated by the magnet 112. In addition, ff the direction of the current applied to the coil 110 is changed in turn, the magnet 112 performs a linear reciprocating movement changing the flux direction of the coil 110. Then, the magnet frame 114 in which the magnet 112 is fixed, performs a linear reciprocating movement so that the operating unit such as a piston and the like performs a linear reciprocating movement.
Here, an eddy current is generated in the circumferential direction of the magnet frame 110 by the linear reciprocating movement of the magnet 108 and the eddy current loss is attenuated by the slit 118 which is formed in the magnet mounting portion 112.
However, in the conventional reciprocating motor, the slit formed to attenuate eddy current loss generated in driving the motor, is formed in the shape of a stripe having a narrow width and accordingly, there occurs a problem that molding accuracy is lowered since the slit is deformed by the compressing stress generated in the circumferential direction of the magnet frame in the molding operation, and it is difficult to maintain roundness of the magnet frame.
Also, when the magnet performs a linear reciprocating movement, a force is applied to the magnet frame in the direction of the length by inertia of the magnet and an edge crack is generated in an edge portion of the slit by the force applied to the magnet frame.
Also, when a slit is processed in the magnetic frame, the slit is formed by the punching operation using a punch or die. Since the width of the slit is narrow and thin, and the width of the punch for the punching operation is also narrow and the thickness of the punch is thin, there occurs a problem that the punch and die are damaged in the processing.